Michael Matthews out of Tour de France

Australia's Michael Matthews is out of the Tour de France with the Canberran forced to pull out of the race less than an hour before the start of the fifth stage due to illness.

The Sunweb rider, last year's green point jersey winner, woke with a fever and reluctantly pulled the pin following advice from team doctors.

"Early this morning, the doctor had an early call from (Matthews) to say that he had to throw up," said Sunweb sports director Luke Roberts.

"He had difficulty getting back to sleep and couldn't eat his breakfast, and the fever is developing more and more.

"We've had a doctor with him all morning, just monitoring his progress.

"He was isolated from the rest of the team, just in case something could spread.

"The doctors monitored him and saw his condition was going downhill. He has a fever that is continuing to rise, so he's not in a condition to start a bike race. The doctors made the decision not to start him."

(AAP )

Meanwhile, Richie Porte has edged his way up to 12th spot following a gruelling 205km fifth stage across the rugged hills of Finestere from Lorient to Quimper.

World champion Peter Sagan won his second stage of the race on Wednesday, outsprinting Italian Sonny Colbrelli (Bahrain-Merida) and Belgian Philippe Gilbert (Quick-Step) in a thrilling finish.

"It was a really good sprint," Sagan said.

"Gilbert attacked and I was well placed. He went early and Colbrelli and I launched our sprint at the right moment. Sonny almost beat me but I crushed the pedals harder."

Thursday's sixth stage has a similar profile but a harder uphill finish in Mur de Bretagne where Sagan may struggle to take a third stage win in 2018.

Porte, who lost 51 seconds in the opening stage after being caught behind a pile-up, has since climbed steadily up the general classification which is still led by his BMC teammate Greg Van Avermaet.

The Tasmanian is 53 seconds behind the Belgian but sits four seconds clear of reigning champion Chris Froome.

Van Avermaet took advantage of an intermediate bonus sprint to add two seconds to his overall lead ahead of another BMC rider Tejay van Gardeeen.

Porte will aim to make up more time in another hilly ride across Britanny on Thursday - the 181km stage between Brest and Mur-de-Bretagne Guerledan.